1. Technical Field
The present invention relates to a radiation system for treating patients with certain skin conditions, such as skin cancer; and more particularly, it relates to a low energy or superficial x-ray radiation therapy system equipped with x-ray filters for regulating the characteristics of the radiation.
2. Discussion of Related Art
So-called superficial x-rays are low energy x-rays useful for treating certain disease conditions occurring typically just below the skin, conditions such as skin cancers and dermatological disorders. A superficial radiation therapy system includes an X-ray tube and a filter so as to deliver most of the radiation at or just below the skin surface. In superficial radiation therapy treatment, an X-ray dose is provided to a patient by providing X-rays at a desired energy and at a desired intensity for a desired time, and by situating the patient at a desired distance from the X-ray tube. Commercially available superficial x-ray therapy systems, such as PHILIPS RT.-100, THERAPAX 150 and GULMAY D3150, have a radiation assembly with several adjustable voltages (in kilovolts), i.e. the voltage between the cathode and the anode of the X-ray tube, and corresponding current (in milliamps). For example the PHILIPS RT-100 has settings of 10/8, 20/10, 30/10, 37/10, 45/10, 55/10 70/10, 85/8, and 100/8 kV/mA. The skin area of the patient to receive the X-ray dose is typically situated a distance of from 10 cm to 25 cm from a focal spot within the X-ray tube. The skin area is positioned relative to the X-ray tube using what is called an applicator, which attaches to a housing for the X-ray tube.
A control panel is used to indicate the desired X-ray energy and intensity level, based on a periodic calibration of the radiation therapy system usually performed from time to time by a health physicist.
In providing an X-ray dose to a patient, as mentioned above a filter is normally used. It is often made with a metal such as copper or aluminum. Some low energy radiation is absorbed in the filter plate, and the radiation passing through the filter has a narrower spectrum. In existing superficial radiation treatment systems such as PHILIPS RT-100, there are as many as nine filters in varying materials and thickness, each is used for one particular voltage/current setting of the x-ray tube. A user (i.e. an operator of the X-ray therapy system) sets up a filter according to the X-ray tube setting by inserting a filter plate. An incorrect insertion of a filter can result in improper radiation level—i.e. a rate of irradiation, in e.g. roentgens per unit time—and also radiation that is shifted in its average energy, and so can lead to an improper dose being delivered to the patient.
The radiation dose provided by the X-ray tube can also vary from what is intended even if the filtering is as intended and even if the last calibration was performed correctly, because the characteristics of the X-ray tube can change over time due to normal wear and tear, and due to environmental factors (e.g. temperature cycling or changes), or the X-ray tube can simply malfunction.
The actual delivered radiation level should typically be within about 5% of the intended radiation level (in e.g. roentgens per unit time), and if it is determined that the actual radiation level differs by more than about 5%, the radiation therapy system must usually be serviced because such a difference can cause the therapy to be either ineffective (if the level is too low by more than 5%) or even unnecessarily harmful (if the level is too high).
What is needed is a simple way to check the radiation level before treating a patient. Since the radiation level depends on the radiation level provided by the radiation assembly (including any filtering) and also the applicator being used, the radiation level should be checked, and the applicator identity should be confirmed.